I can only say whats worked for me over many years and manyyyyyyyyyyy tractors (was a used tractor dealer)
NOT ALWAYS MIND YOU LOL BUT HERES THE BEST IN MY OPINION........ After I cleaned/ground down/polished or whatever it took to get to a good shiny (no paint or grease or rust) conductive case/frame member. I used stainless steel bolts nuts and the biting barbed star lock washers and good soldered and crimped terminals with heat shrink etc wires and terminations, then when all is done if you keep oxygen and moisture away oxidation/rust is greatly reduced, so a thin coat of silicone or other coating, then let it dry then paint over.
If you do it that way I neverrrrrrrr had connection problems later. Similar on battery posts if you use the felt washers underneath then top it all off with that red terminal coating I NEVER HAD CONNECTIONS GO BAD
Thats my story n Ima stickin to it,,,,,,clean bright shiny steel,,,,,,,stainless steel star lock washers and other hardware,,,,,,,,,soldered and crimped terminals,,,,,,,,,,,coat all to keep air and water away YOURE GOOD TO GO